Epitaxial gallium arsenide wafers

The preparation of GaAs epitaxial layers by a vapor transport process using AsCl3, Ga and H2 was pursued to provide epitaxial wafers suitable for the fabrication of transferred electron oscillators and amplifiers operating in the subcritical region. Both n-n(+) structures, and n(++)-n-n(+) sandwich structures were grown using n(+) (Si-doped) GaAs substrates. Process variables such as the input AsCl3 concentration, gallium temperature, and substrate temperature and temperature gradient and their effects on properties are presented and discussed

The Effects of Prehydration on Cement Performance

This study investigated the effects of cement prehydration on cement’s engineering properties. Anhydrous cement was exposed over a saturated KCl solution to maintain 85% RH, for 7 and 28 days. Mortar and cement pastes were tested for strength, workability and setting time, with sample analysis by XRD and DTA. Results showed a decreased reactivity of the prehydrated cements resulting in reduced strength and increased setting times. We propose that this may be due to an upset of the sulphate balance in the cement upon prehydration

Factorial Design Applied to Waste Immobilisation in Geopolymer-based Systems

Concentrated alkali, ground glass and air pollution control residues were mixed in various proportions and cured for up to 28 days. These blocks were tested in strength and analysed by thermal gravimetric analysis to assess the success of the geopolymerisation process. A Taguchi factorial design approach was then adopted to investigate the effects of different variables upon the strength development of these blocks

Structure, bonding and morphology of hydrothermally synthesised xonotlite

The authors have systematically investigated the role of synthesis conditions upon the structure and morphology of xonotlite. Starting with a mechanochemically prepared, semicrystalline phase with Ca/Si=1, the authors have prepared a series of xonotlite samples hydrothermally, at temperatures between 200 and 250 degrees C. Analysis in each case was by X-ray photoelectron spectroscopy, environmental scanning electron microscopy and X-ray diffraction. The authors’ use of a much lower water/solid ratio has indirectly confirmed the ‘through solution’ mechanism of xonotlite formation, where silicate dissolution is a key precursor of xonotlite formation. Concerning the role of temperature, too low a temperature (~200 degrees C) fails to yield xonotlite or leads to increased number of structural defects in the silicate chains of xonotlite and too high a temperature (>250 degrees C) leads to degradation of the xonotlite structure, through leaching of interchain calcium. Synthesis duration meanwhile leads to increased silicate polymerisation due to diminishing of the defects in the silicate chains and more perfect crystal morphologies

Recent achievements in cereal feed grains nutrition

Dissertação de mestrado em Psicologia da Educação, Desenvolvimento e Aconselhamento, apresentada à Faculdade de Psicologia e de Ciências da Educação da Universidade de CoimbraEste trabalho tem como objectivo conhecer o processo de adaptação das crianças e jovens em risco ao acolhimento prolongado em Lares de Infância e Juventude, através das diferentes vivências que estas experienciam ao longo do acolhimento institucional. Tentou-se igualmente perceber de que modo esta experiência de vida influenciou a percepção que os adolescentes tinham de si próprios. Embora alguma investigação, muita de natureza qualitativa, tenha vindo a procurar identificar as necessidades das crianças e jovens institucionalizados e aceder às suas experiências de vida, a investigação acerca do percurso vivido durante a instituicionalização ainda é escassa e merece uma análise mais pormenorizada. Com recurso à metodologia da Grounded Theory, partiu-se da recolha de narrativas de nove adolescentes institucionalizados, 6 raparigas e 3 rapazes, com uma média etária de 17, 7 anos (DP= 1,15), levadas a cabo em três Lares de Infância e Juventude. A análise destas narrativas permitiu identificar a existência de quatro fases de adaptação ao acolhimento prolongado de crianças e jovens em risco: fase de (des)amparo, fase da revolta, fase da resignação e fase da pré-autonomia. Em todas estas fases o sofrimento devido à separação da família é reflectido de alguma forma e o sentimento de ligação, de suporte e de partilha parece ser a melhor forma de atenuar esta dor em todas as fases e permitir uma melhor autonomia de vida ao sair da instituição.This work aims to study the process of adaptation of children and young people at risk to extended placement in Childhood and and Youth Homes, by looking into the different experiences they go through during institutional care. It was also a goal to understand in which way this experience had influenced the perception they have about themselves.. Although the research, essentially of qualitative nature, has been seeking to identify the needs of children and young people in residential care and to have access to their life experiences, research about the the time lived in institutions is still scarce and deserves a more detailed analysis. Through Grounded Theory procedures, the narratives of nine institutionalized adolescents, 6 girls and 3 boys with a mean age of 17,7 years (DP= 1,15) undertaken in three Childhood and and Youth Homes. The analysis of these narratives identified the existence of four stages of adaptation to extended placement of children and young people at risk: phase of (un)support, phase of revolt, phase of resignation and phase of preautonomy. In all these phases the suffering due to separation from family is reflected in some way and the feeling of connection, sharing and support seems to be the best way to alleviate this pain at all stages and allow greater autonomy of life to get out of the institution

The influence of social interaction on cognitive remediation for schizophrenia

In addition to the core features of the condition, individuals with schizophrenia typically exhibit deficits in cognitive functions (Barnett et al., 2010). Such impairments are known to be important determinants of functional outcome (Green et al., 2000; Harvey et al., 2003) and their magnitude is associated with the level of self-care, utilization of hospital services, and burden placed on caregivers (Davidson and Keefe, 1995; Sevy and Davidson, 1995; Martens and Addington, 2001). The cognitive features of schizophrenia are poorly treated with antipsychotics (Liberman, 1994). Cognitive training offers a more promising option. Training interventions have been associated with cognitive improvements including information processing, verbal learning, and executive function (Medalia et al., 1998; Bellucci et al., 2003; McGurk et al., 2005; Sartory et al., 2005). The most recent meta-analysis found that, for individuals with schizophrenia, cognitive training improves cognitive function, psychosocial function, and psychiatric symptom severity (effect sizes of 0.45, 0.42, and 0.18 respectively; Wykes et al., 2011). Such findings highlight the promise of training programs in treating the cognitive symptoms of schizophrenia

High-temperature optically activated GaAs power switching for aircraft digital electronic control

Gallium arsenide high-temperature devices were fabricated and assembled into an optically activated pulse-width-modulated power control for a torque motor typical of the kinds used in jet engine actuators. A bipolar heterojunction phototransistor with gallium aluminum arsenide emitter/window, a gallium arsenide junction field-effect power transistor and a gallium arsenide transient protection diode were designed and fabricated. A high-temperature fiber optic/phototransistor coupling scheme was implemented. The devices assembled into the demonstrator were successfully tested at 250 C, proving the feasibility of actuator-located switching of control power using optical signals transmitted by fibers. Assessments of the efficiency and technical merits were made for extension of this high-temperature technology to local conversion of optical power to electrical power and its control at levels useful for driving actuators. Optical power sources included in the comparisons were an infrared light-emitting diode, an injection laser diode, tungsten-halogen lamps and arc lamps. Optical-to-electrical power conversion was limited to photovoltaics located at the actuator. Impedance matching of the photovoltaic array to the load was considered over the full temperature range, -55 C to 260 C. Loss of photovoltaic efficiency at higher temperatures was taken into account. Serious losses in efficiency are: (1) in the optical source and the cooling which they may require in the assumed 125 C ambient, (2) in the decreased conversion efficiency of the gallium arsenide photovoltaic at 260 C, and (3) in impedance matching. Practical systems require improvements in these areas

Is there overutilisation of cataract surgery in England?

<b>Objectives:</b> Following a 3.7-fold increase in the rate of cataract surgery in the UK between 1989 and 2004, concern has been raised as to whether this has been accompanied by an excessive decline in the threshold such that some operations are inappropriate. The objective was to measure the impact of surgery on a representative sample of patients so as to determine whether or not overutilisation of surgery is occurring. <b>Design:</b> Prospective cohort assessed before and 3 months after surgery. <b>Setting:</b> Ten providers (four NHS hospitals, three NHS treatment centres, three independent sector treatment centres) from across England. <b>Participants:</b> 861 patients undergoing first eye (569) or second eye (292) cataract surgery provided preoperative data of whom 745 (87%) completed postoperative questionnaires. <b>Main outcome measures:</b> Patient-reported visual function (VF-14); general health status and quality of life (EQ5D); postoperative complications; overall view of the operation and its impact. <b>Results:</b> Overall, visual function improved (mean VF-14 score increased from 83.2 (SD 17.3) to 93.7 (SD 13.2)). Self-reported general health status deteriorated (20.3% fair or poor before surgery compared with 25% afterwards) which was reflected in the mean EQ5D score (0.82 vs 0.79; p = 0.003). At least one complication was reported by 66 (8.9%) patients, though this probably overestimated the true incidence. If the appropriateness of surgery is based on an increase in VF-14 score of 5.5 (that corresponds to patients’ reporting being "a little better"), 30% of operations would be deemed inappropriate. If an increase of 12.2 (patients’ reports of being "much better") is adopted, the proportion inappropriate is 49%. Using a different approach to determining a minimally important difference, the proportion inappropriate would be closer to 20%. Although visual function (VF-14) scores were unchanged or deteriorated in 25% of patients, 93.1% rated the results of the operation as "good," "very good" or "excellent," and 93.5% felt their eye problem was "better." This partly reflects inadequacies in the validity of the VF-14. <b>Conclusions:</b> Improvement in the provision of cataract surgery has been accompanied by a reduction in the visual function threshold. However, methodological difficulties in measuring the impact of cataract surgery on visual function and quality of life mean it is impossible to determine whether or not overutilisation of cataract surgery is occurring. N Black1, J Browne1, J van der Meulen1, L Jamieson2, L Copley2 and J Lewsey